Heretofore, the combination of a travelling grate reactor furnace, a shaft furnace and a fixed bed gasifier has been operated by feeding limited amounts of air and/or steam upwardly through a coal bed on the travelling grate so as to drive off most of the volatiles in the coal, almost all of the remainder of which volatiles were driven off by residual heat as the incandescent coal from the travelling grate reactor moved downwardly through the shaft furnace. The volatile-laden gases from the travelling grate reactor and shaft furnaces were exhausted from the top of the traveling grate reactor through a common flue and the product gas from the fixed bed gasifier was fed to a utilization device such as a boiler. This entailed certain problems in that care was needed to insure that air does not enter the shaft furnace, lest the fixed carbon in the partially gasified coal be burned there, rather than in the fixed bed gasifier. A lock hopper was interposed between the shaft furnace and the fixed bed gasifier and this needed expensive valves made of exotic materials. It also imposed certain limitations on the lump size of the hot carbon and, in addition, fine and coarse materials tended to segregate and this, in turn, upset the operation of the fixed bed gasifier, and plugging of the valves constantly interrupted the operation. Furthermore, as the hot incandescent carbon drops off the end of the travelling grate into the shaft furnace, a veritable inferno of hot flying particles is created, and when these were induced into the gas stream exhausted from the atmosphere of the travelling grate reactor furnace, particulate pollution resulted.